J-Us was born Lee Seungjoon 이승준 on January 13, 1995, in Seoul. He was born only 10 days before fellow ONF member Wyatt.

He and E-tion are both Capricorns. He was born in the Year of the Dog. J-Us, MK, U, and Laun’s blood type is AB.

J-Us, U, and E-tion speak Japanese.

He was a WM Ent. trainee for five years. He appeared with Wyatt and Laun in B1A4’s concert video “The Class.” Along with Hyojin, E-tion, and Wyatt, he performed as a dancer on the web drama “Loss:Time:Life.” He and all of the ONF members competed on the show “MixNine.”

He’s the leader of the ONF sub-unit Off.

When he was younger, he wanted to be a table tennis player. Throughout high school, he was the vice-president of the student committee. For fun, he watches dramas. He likes eating port with noodles. He doesn’t like bell peppers.